This invention relates generally to an apparatus for processing the signals from a device which detects the operating state of an engine, and particularly to an apparatus which converts detection signals that pulsate in correspondence to the rotation of the engine to signals from which the pulsation has been removed to thereby accurately indicate the operating state of the engine based on the air intake volume or the intake pipe pressure for accurate electronic control of the engine.
For example, when the fuel injection amount and the ignition timing, etc., are electronically controlled by an engine control unit using a microcomputer, the operating state of the engine is detected and the control unit calculates a suitable amount of fuel to be injected and a suitable injection timing for the operating state of the engine based on these detection signals. Various sensors are used to detect the operating state of the engine such as an intake air sensor provided in the intake air pipe for supplying air to the engine and a pressure sensor for detecting the air pressure in the intake pipe.
The quantity and pressure of the air flowing in the intake pipe, however, varies in response to the cycle of the engine so the detection signal pulsates. Accordingly, these pulsating detection signals cannot be used as is and cannot be supplied directly to the control unit and used in calculating the engine control data.
It has, consequently, been considered desirable to eliminate the pulsating component in the detection signals using an averaging circuit or an active filter circuit, for example, converting these signals to suitable digital signals and supplying them to the control unit, which comprises a microcomputer, as input data. Another possibility that has been considered is synchronizing the signals with a specific crankshaft rotation angle, A/D converting the signals, extracting level data of the portion corresponding to the phase of the pulsating detection signal and using these extracted signals as the detection signals.
However, using such means to take out the measurement signals of the air volume, for example, results in a delay when there is an abrupt change in the operating state of the engine, such as during rapid acceleration. When the detection signals are synchronized with the crankshaft angle, there is an inevitable deviation between the crankshaft angle and the pulsating signal so that these signals lack accuracy.